From Wikipedia

China A Century Of Revolution

The Chinese Civil War
was fought between the Kuomintang (KMT or Chinese Nationalist Party) and the Communist Party of China (CPC).

The war began in April 1927, amidst the Northern Expedition,. The war represented an ideological split between the Western-supported Nationalist KMT and the Soviet-supported Communist CPC. In communist historiography the war was also known as the "War of Liberation"
The civil war carried on intermittently until the Second Sino-Japanese War interrupted it, resulting in the two parties forming a Second United Front. The Japanese assault and occupation of Eastern China was an opportunistic attack made possible by China's internal turmoil. Japan's campaign was defeated in 1945, marking the end of World War II, and China's full-scale civil war resumed in 1946. After a further four years, 1950 saw a cessation of major hostilities—with the newly founded People's Republic of China controlling mainland China (including Hainan Island), and the Republic of China's jurisdiction being restricted to Taiwan, Penghu, Kinmen, Matsu and several outlying Fujianese islands. To this day, since no armistice or peace treaty has ever been signed, there is controversy as to whether the Civil War has legally ended, even though the two sides have close economic ties.